The present invention relates to a refrigerating device using a working medium containing an R32 refrigerant (chemical formula: CH2F2) and particularly to a refrigerating device which copes with a low GWP (global warming potential), is energy-saving and inexpensive, and is capable of protecting the ozone layer and achieving recycling.
Hitherto, a refrigerating device of the heat pump type using a HCFC (hydrochlorofluorocarbon) refrigerant is known. The refrigerating device has a refrigerant circuit having a compressor, a condenser, a motor operated valve, and an evaporator connected sequentially in the shape of a loop and has a supercooling heat exchanger disposed between the condenser and the motor operated valve. A gas refrigerant from the supercooling heat exchanger is returned to a liquid injection of the compressor and the suction side of the compressor. However the refrigerating device has a problem of deterioration of the COP (coefficient of performance) owing to decrease in the circulation amount of the refrigerant caused by by-passing of the refrigerant. The HCFC refrigerants have a problem of deteriorating the environment of the earth because they have a high ozone-layer destruction coefficient and a high GWP (global warming potential).
Thus it is conceivable to use the R32 refrigerant as a low-GWP HFC refrigerant capable of realizing a high COP without destroying the ozone layer. However in its physical properties, the R32 refrigerant has a higher discharge temperature than the HCFC refrigerants. Thus the R32 refrigerant has a problem that it deteriorates oil for the refrigerating device so that the reliability deteriorates.
In a conventional apparatus using R22, when a dryness of the refrigerant at the suction side of a high-pressure dome type compressor is 0.97, the discharge temperature reaches 90xc2x0 C. In the case of a low-pressure dome type compressor, when a dryness of the refrigerant at its suction side is 0.97, the discharge temperature reaches 70xc2x0 C.
The R32 refrigerant has a low pressure loss and its COP (coefficient of performance) can be improved, whereas in its physical properties, its discharge temperature rises to a temperature higher than the discharge temperatures of R22, R410, and R407 by 15xc2x0 C. in theory and by 10-15xc2x0 C. in actual measurement. Thus in an apparatus using R22, R410 or R407, merely replacing such a refrigerant with R32 and changing the refrigeration oil to an oil compatible with R32 would lead to a problem of deterioration in reliability and performance.
Regarding the reliability, there is a fear that when the compressor is heated to a high temperature, deterioration of a material and oil proceeds and its long-term reliability deteriorates. In particular, because a compressor motor deteriorates (the demagnetizing force decreases) greatly owing to temperature, attention should be paid to a DC motor in dependence on a material that is used therefor.
Regarding the performance, supposing that the discharge-pipe temperature, the manner of controlling the refrigerant by using sensors, and the manner of controlling electric current are same as before, the R32 refrigerant has a problem of deteriorating the performance of the refrigerating device and reducing its operation area.
Therefore, it is an object of the present invention to provide a refrigerating device capable of optimizing the discharge temperature of a compressor without deteriorating the efficiency of the compressor by using a working medium containing an R32 refrigerant, so that the COP and reliability of the refrigerating device is improved.
In order to accomplish the above object, a refrigerating device according to the present invention comprises:
a refrigerant circuit having a compressor, a condenser, a main pressure-reducing means, and an evaporator connected in a loop;
a supercooling heat exchanger disposed between the condenser and the main pressure-reducing means;
a by-pass pipe by which a gas side of the refrigerant circuit and a liquid side thereof are connected through the supercooling heat exchanger; and
a supercooling pressure-reducing means disposed at the by-pass pipe upstream of the supercooling heat exchanger, wherein:
the refrigerating device uses an R32 refrigerant or a mixed refrigerant containing the R32 refrigerant at at least 70 wt %; and
the refrigerating device further comprises:
a discharge temperature sensor detecting a discharge temperature of the compressor;
a discharge temperature determination part determining the discharge temperature detected by the discharge temperature sensor; and
a control part controlling the supercooling pressure-reducing means, based on a result of determination made by the discharge temperature determination part, to control an amount of the refrigerant flowing through the by-pass pipe.
According to the refrigerating device, after the R32 refrigerant (or the mixed refrigerant containing R32 at at least 70 wt %) discharged from the compressor is condensed by the condenser, the refrigerant is pressure-reduced by the main pressure-reducing means. Then the refrigerant vaporizes in the evaporator and returns to the suction side of the compressor. At this time, the refrigerant pressure-reduced by the supercooling pressure-reducing means flow from the liquid side of the refrigerant circuit to the gas side thereof at the downstream side of the evaporator by the by-pass pipe through the supercooling heat exchanger. The supercooling heat exchanger supercools the refrigerant flowing from the condenser to the main pressure-reducing means. The discharge temperature determination part determines the discharge temperature detected by the discharge temperature sensor. Based on the result of the determination, the control parts controls the supercooling pressure-reducing means to adjust the amount of the refrigerant flowing through the by-pass pipes to a large amount or a small amount, according as the discharge temperature is high or low. Thus, when the discharge temperature is high, the discharge temperature can be decreased by increasing the amount of the refrigerant flowing through the by-pass pipes. Accordingly, even if the R32 refrigerant (or the mixed refrigerant containing R32 at at least 70 wt %) which is higher, due to its physical property, in the discharge temperature than the HCFC refrigerants is used, it is possible to optimize the discharge temperature without deteriorating the efficiency and thus improve the COP and the reliability. A motor operated valve may be used as the supercooling pressure-reducing means. Then, the opening of the motor operated valve is controlled to control a by-pass refrigerant amount. Further a solenoid operated valve and a capillary may be combined to provide the supercooling pressure-reducing means to control the by-pass refrigerant amount by opening and closing of the solenoid operated valve.
In one embodiment, when the discharge temperature determination part determines that the discharge temperature exceeds a set upper-limit value, the control part controls the supercooling pressure-reducing means to increase the amount of the refrigerant flowing through the by-pass pipe, and to decrease the amount of the refrigerant flowing through the by-pass pipe when the discharge temperature determination part determines that the discharge temperature is smaller than a set lower-limit value.
According to the refrigerating device, when the discharge temperature determination part determines that the discharge temperature exceeds a set upper-limit value, the control part controls the supercooling pressure-reducing means to increase the amount of the refrigerant flowing through the by-pass pipe. On the other hand, when the discharge temperature determination part determines that the discharge temperature is smaller than the set lower-limit value, the control part controls the supercooling pressure-reducing means to decrease the amount of the refrigerant flowing through the by-pass pipe. Thereby optimum control of the discharge temperature can be accomplished without deteriorating the efficiency.
In another embodiment, the supercooling pressure-reducing means comprises a supercooling motor operated valve, and the refrigerating device further comprises a condensation temperature sensor detecting a condensation temperature of the condenser; an evaporation temperature sensor detecting an evaporation temperature of the evaporator; and a target discharge temperature computing part computing a target discharge temperature, based on the condensation temperature detected by the condensation temperature sensor, the evaporation temperature detected by the evaporation temperature sensor, and an opening of the supercooling motor operated valve. The control part controls the main pressure-reducing means to allow the discharge temperature of the compressor to attain to the target discharge temperature.
According to the refrigerating device, based on the condensation temperature of the condenser detected by the condensation temperature sensor, the evaporation temperature of the evaporator detected by the evaporation temperature sensor, and the opening of the supercooling motor operated valve, the target discharge temperature computing part computes the target discharge temperature suitable to the operation conditions or situation (cooling operation/heating operation, operation frequency of the compressor, etc.). Based on the target discharge temperature computed by the target discharge temperature computing part, the control part controls the main pressure-reducing means to control the amount of the refrigerant flowing through the refrigerant circuit so that the discharge temperature of the compressor attains to the target discharge temperature. Thus, optimum control of the discharge temperature can be accomplished according to the amount of the refrigerant flowing through the by-pass pipe, namely, a supercooling degree.
In one embodiment, the refrigerating device further comprises an evaporator-exit temperature sensor detecting a temperature at an exit of the evaporator. The control part controls the main pressure-reducing means and the supercooling motor operated valve, based on the target discharge temperature computed by the target discharge temperature computing part and the temperature at the exit of the evaporator detected by the evaporator-exit temperature sensor.
According to the refrigerating device, the evaporator-exit temperature sensor detects the temperature at the exit of the evaporator. Based on the target discharge temperature computed by the target discharge temperature computing part and the temperature at the exit of the evaporator detected by the evaporator-exit temperature sensor, the control part controls the main pressure-reducing means and the supercooling pressure-reducing means. By using the temperature at the exit of the evaporator to control the discharge temperature of the compressor, it is possible to improve controllability of the amount of the refrigerant flowing through the by-pass pipe, namely, controllability of the supercooling degree.
Generally, as shown with a P-H (pressure-enthalpy) diagram in FIG. 12, a maximum temperature in a refrigerating cycle is a temperature at the discharge side of the compressor.
The present inventors ascertained in experiments that when the R32 refrigerant is used, the reliability of the compressor is ensured, even though a superheat SH is decreased to increase the wetness of the R32 refrigerant, as shown with a P-H (Td3-Tcu3) line of FIG. 13, as compared with a conventional (Td1-Tcu1) line. As shown in FIG. 13, when the wetness of the R32 refrigerant at the suction side of the compressor is increased, a temperature Td at the discharge side of the compressor decreases from Td1 to Td3. Thus it is possible to avoid reduction in the reliability and the performance.
Let the wetness be x, the refrigerant is in a complete gaseous state when x=1.0, in a liquid state when x=0, and in a fluidized state, or a state of two phases, when x=0.5, 0.6, 0.9, and so on. Supposing that the dryness is y, y=1xe2x88x92x.
As shown in test results of reliability of FIG. 11, in the case where the conventional R22 refrigerant was used, the reliability of the compressor was at an unusable level unless the dryness thereof at the suction side of the compressor was 0.90 or more. In the case of the R32 refrigerant, it was confirmed in experiments that when the dryness thereof at the suction side of the compressor was not less than 0.60, the reliability of the compressor was at a usable level.
Accordingly, in one embodiment, a compressor sucks and compresses an R32 refrigerant having a dryness of 0.65 or more or a mixed refrigerant containing R32 at at least 70 wt % and having a dryness of 0.65 or more.
In the embodiment, the compressor sucks and compresses the R32 refrigerant having the dryness of 0.65 or more. Thus, as is apparent from the test results shown in FIG. 11, it is possible to use the R32 refrigerant without deteriorating the reliability of the compressor and realize energy-saving and a low GWP without reducing the reliability and performance. Also in the case where the compressor sucks the mixed refrigerant containing R32 at 70 wt % or more and having the dryness of 0.65 or more as well, similar effects can be obtained.
In another embodiment, a compressor sucks and compresses an R32 refrigerant having a dryness of 0.70 or more or a mixed refrigerant containing R32 at at least 70 wt % and having a dryness of 0.70 or more.
In the embodiment, since the compressor sucks the R32 refrigerant having the dryness of 0.70 or more, the reliability of the compressor can be further improved. In the case where the compressor sucks the mixed refrigerant containing R32 at at least 70 wt % and having the dryness of 0.70 or more, similar effects can be obtained.
That is, a mixed refrigerant containing R32 at at least 70 wt % provides a pseudo-azeotropy, which allows the R32 refrigerant to have advantages (energy-saving and low GWP) over the R22 refrigerant.
In one embodiment, a compressor sucks and compresses an R32 refrigerant having a dryness of 0.75 or more or a mixed refrigerant containing R32 at at least 70 wt % and having a dryness of 0.75 or more.
In the embodiment, since the compressor sucks the R32 refrigerant having the dryness of 0.75 or more, the reliability of the compressor can be enhanced to a maximum level as is apparent from the test results shown in FIG. 11. In the case where the compressor sucks the mixed refrigerant containing R32 at at least 70 wt % and having the dryness of 0.75 or more as well, similar effects can be obtained.
In one embodiment, the refrigerating device comprises a control means detecting a discharge-pipe temperature of the compressor and controlling the dryness of the refrigerant sucked by the compressor based on the detected discharge-pipe temperature.
In the embodiment, the dryness of the refrigerant sucked by the compressor is controlled based on the discharge-pipe temperature of the compressor. Thus the dryness can be controlled by the simple control means.
In one embodiment, the refrigerating device comprises a control means detecting a superheat and controlling the dryness of the refrigerant sucked by the compressor based on the detected superheat.
In the embodiment, the dryness of the refrigerant sucked by the compressor is controlled based on the superheat. Thus, the dryness of the suction side can be controlled with high precision and the reliability of the compressor can be improved.
In another embodiment, the refrigerating device comprises a control means detecting a subcooling degree and controlling the dryness of the refrigerant sucked by the compressor based on the detected subcooling degree. In the embodiment, the dryness of the refrigerant sucked by the compressor is controlled based on the subcooling degree. Thus the dryness at the suction side can be controlled with high precision and the reliability of the compressor can be improved.
In one embodiment, the refrigerating device comprises a control means controlling a superheating degree at an exit of an evaporator. In the embodiment, the superheating degree at the exit of the evaporator is controlled to increase the wetness at the exit of the evaporator. Thus it is possible to prevent condensation on a fan rotor of the evaporator (in an indoor unit).
In another embodiment, a compressor is of a high-pressure dome type, and in a heating operation at a low temperature (for example, the outdoor temperature is xe2x88x925xc2x0 C. or below), the compressor sucks and compresses an R32 refrigerant having a dryness of 0.68 or more or a mixed refrigerant containing R32 at at least 70 wt % and having a dryness of 0.68 or more; and a discharge temperature of the compressor is set to 80-90xc2x0 C.
In the embodiment, the dryness of the R32 refrigerant at the suction side of the high-pressure dome type compressor is set to 0.68 or more, and the discharge temperature is set to 80-90xc2x0 C. Thus it is possible to use the R32 refrigerant without deteriorating the reliability of the compressor, which realizes energy-saving and a low GWP and avoids deterioration of the reliability and performance.
In one embodiment, a compressor is of a low-pressure dome type, and in a heating operation at a low temperature (for example, the outdoor temperature is xe2x88x925xc2x0 C. or below), the compressor sucks and compresses an R32 refrigerant having a dryness of 0.65 or more or a mixed refrigerant containing R32 at at least 70 wt % and having a dryness of 0.65 or more; and a discharge temperature of the compressor is set to 60-70xc2x0 C.
In the embodiment, the dryness of the R32 refrigerant at the suction side of the low-pressure dome type compressor is set to 0.65 or more, and the discharge temperature is set to 60-70xc2x0 C. Thus it is possible to use the R32 refrigerant without deteriorating the reliability of the compressor, which realizes energy-saving and a low GWP and avoids deterioration of the reliability and performance.